1. Field of the Invention
The present invention relates to a method for handling anaerobic digestion effluent. In particular, it relates to a method for treating the effluent in a high solids digestion to produce a biogas and a semi-solid secondary digestate.
2. Description of Related Art
The anaerobic digestion of organic material such as sewage sludge, municipal waste, industrial waste forest waste, agricultural waste, and especially animal waste is the fermentation of such material by bacteria in the absence of oxygen. The benefit of such digestion of waste material includes the stabilization of waste, odor control, solid reduction, energy production in the form of methane gas, elimination or reduction of pathogens, making the waste more environmentally neutral, producing a nutrient source, and the like. It has been generally used in many large scale treatments of animal wastes to control the disposal problem associated with such waste.
However, after the completion of the anaerobic digestion, the management of the effluent is a challenge. The volume of effluent is typically very large and large tracts of farm land are generally utilized to take the liquid for irrigation and fertilizer. Because of the high Biochemical Oxygen Demand (BOD)/Chemical Oxygen Demand (COD) and ammonium contents of this type of liquid waste, it is not generally allowed to be discharged into natural water streams or other bodies of water. Accordingly, management of the effluent is a constant concern and management problem and has even caused operations to shut down for lack of a management solution.